We recently reported (James et al,1999, Hair as a Diagnostic Tool for Breast Cancer. Nature 328:33-34) very exciting results of experiments performed partly on the BioCAT beamline that demonstrated a correlation between the presence of breast cancer and the appearance of additional features in fiber diffraction patterns from hair from these individuals. These features appear to be associated with membranous components in the hair. Studies are underway to determine the exact nature of these changes and to see how they relate to various types of breast cancers and stage of development of the disease. These findings indicate the potential for a relatively cheap, convenient and non-invasive screening method for the early detection of breast cancer. Similar findings have been found for skin biopsies where the presence of malignancy somewhere in the body is indicated by expression of fetal isoforms of collagen in the adult skin. These latter results have been submitted for publication. Keratin and collagen form complex structures with very weakly diffracting features. These studies benefited greatly from the fine focus (which increases the information content of patterns) and the high flux (which dramatically increases throughput) provided by the BioCAT ID line.